What is pH

pH is a measure of the hydorgen ion concentration of a solution. Solutions with a high concentration of hydrogen ions have a low pH and solutions with a low concentrations of H+ ions have a high pH. This may seem like a confusion way to express these reationships, and it is, until you understand what pH stands for. The equation that defines pH is given as follows:

pH=-log[H+] concentration,

which is read:

the pH is equal to minus the log of the H+ concentration.

For example is the H+ concentration is very low, lets say about 0.0000001M, then the pH is

pH= -log[.0000001] whis is the same as -log[1 X 10-7]

the term log[1 X 10-7] = -7

- (-7) = 7

Look at the following table


 hydrogen ion concetration  pH  solutions with a pH of
 .1M  1  
 .01M  2  coke and orange juice
 .001  3  
 .0001  4  
 .00001  5  black coffee
 .000001  6  
 .0000001  7  pure water
 .00000001  8  
 .000000001  9  baking soda
 .0000000001  10  
 .00000000001  11  
 .000000000001  12  household bleach
 .0000000000001  13  oven cleaner

From this table you will notice a few relationships